Photo-oxidation of tyrosine in a bio-engineered bacterioferritin ‘reaction centre’—A protein model for artificial photosynthesis

• Published in: Biochimica et biophysica acta 2014-10, Vol.1837 (10), p.1821-1834
• Main Authors: Hingorani, Kastoori, Pace, Ron, Whitney, Spencer, Murray, James W., Smith, Paul, Cheah, Mun Hon, Wydrzynski, Tom, Hillier, Warwick
• Format: Article
• Language: English
• Subjects: Artificial photosynthesis; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bacterioferritin; Base Sequence; Cytochrome b Group - chemistry; Cytochrome b Group - metabolism; DNA Primers; Electron Spin Resonance Spectroscopy; Electron transfer; Ferritins - chemistry; Ferritins - metabolism; Models, Molecular; Oxidation-Reduction; Photochemistry; Photosynthesis; Photosystem II; Polymerase Chain Reaction; Protein Engineering; Tyrosine - chemistry; Tyrosine oxidation
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/j.bbabio.2014.07.019

The photosynthetic reaction centre (RC) is central to the conversion of solar energy into chemical energy and is a model for bio-mimetic engineering approaches to this end. We describe bio-engineering of a Photosystem II (PSII) RC inspired peptide model, building on our earlier studies. A non-photosynthetic haem containing bacterioferritin (BFR) from Escherichia coli that expresses as a homodimer was used as a protein scaffold, incorporating redox-active cofactors mimicking those of PSII. Desirable properties include: a di-nuclear metal binding site which provides ligands for bivalent metals, a hydrophobic pocket at the dimer interface which can bind a photosensitive porphyrin and presence of tyrosine residues proximal to the bound cofactors, which can be utilised as efficient electron-tunnelling intermediates. Light-induced electron transfer from proximal tyrosine residues to the photo-oxidised ZnCe6•+, in the modified BFR reconstituted with both ZnCe6 and MnII, is presented. Three site-specific tyrosine variants (Y25F, Y58F and Y45F) were made to localise the redox-active tyrosine in the engineered system. The results indicate that: presence of bound MnII is necessary to observe tyrosine oxidation in all BFR variants; Y45 the most important tyrosine as an immediate electron donor to the oxidised ZnCe6•+ and that Y25 and Y58 are both redox-active in this system, but appear to function interchangebaly. High-resolution (2.1Å) crystal structures of the tyrosine variants show that there are no mutation-induced effects on the overall 3-D structure of the protein. Small effects are observed in the Y45F variant. Here, the BFR-RC represents a protein model for artificial photosynthesis. •E. coli bacterioferritin was bio-engineered as a PSII inspired peptide model.•Binding of ZnCe6 at the dimer interface and MnII at the di-metal site is shown.•Light-induced electron transfer via tyrosine residues to the ZnCe6•+ is observed.•Presence of bound MnII is necessary to observe tyrosine photo-oxidation.•Y45 is an important electron donor; Y25 and Y58 appear to function interchangeably.